1. Field of Invention
This invention relates to high strength paper and to the process manufacturing high strength paper.
2. Description of the Prior Art
Various types of paper, with or without lamination, to achieve enhanced strength, texture, and functionality are known.
For example U.S. Pat. No. 5,993,953 describes a laminated paper, including a water soluble polyvinyl alcohol layer, having selective air permeability and lengthwise softness for application as a cushioning material. The laminated paper comprises a paper base, and water soluble PVA laminated over the entire surface of the paper base, either by using a PVA strain adhesive or by extrusion lamination using a cold water soluble plastic PVA resin.
U.S. Pat. No. 5,958,180 discloses a method of increasing the strength of paper or paperboard product by specially treating the cellulosic fibers to significantly increase their inter fiber bonding strength. The paper made from such fibers exhibits overall improved dimensional stability. Such processes are elaborate and require intricate process steps making them expensive. The use of external adhesive and offline lamination method renders these papers as an expensive proposition.
U.S. Pat. No. 5,786,064 describes an apparatus for producing a breathable high strength paper/plastic film laminate fabric sheeting capable of being cut, sewn to manufacture garments. In this apparatus, a web of metallised paper and a web of oriented synthetic plastic film whose inner surface is corona discharge treated before being coated with a water based adhesive are concurrently fed in superposed relating into combining rolls to effect cold lamination of the webs to yield a laminate sheeting in which the orientation of the film web is unimpaired. The laminate sheeting emerging from the combination rolls is then foraminated to render the sheeting permeable only to moisture vapour, whereby the foraminated sheeting has fabric properties and can be tailored to garments.
U.S. Pat. No. 4,692,211 describes a process for the preparation of high strength cellulosic gel containing kraft paper by mechanically refining kraft papermaking pulp to an appropriate freeness, mixing the resulting refined pulp with hydrated cellulosic gel binder running the resulting fluid into a felted sheet and pressing and drying the sheet to form the kraft paper product.
U.S. Pat. No. 5,694,702 teaches the art of enhancing cross-directional stretch and tensile energy absorption during paper manufacture. An unrestrained drying capability is added to an existing series of rotating drying cylinders in a cost and space efficient manner to achieve the desired result.
It is clear from the existing prior art that the methods for strengthening paper are complex involving the use of selective adhesives, extrusion lamination, fiber strengthening, coating using cold lamination, laminate sheeting followed by its formation, mechanically refining kraft paper pulp followed by mixing of hydrated cellulosic gel binder and enhancing cross directional stretch by unrestrained drying etc.
The long felt need of the paper industry especially involving manufacturing of bank note papers, paper based security products, packaging require non tamperable high strength paper that is capable of being processed by diverse means. None of the methods described in the prior art or in current practice are capable of making paper of the desired strength and security parameters in a simple and cost effective manner.
The present invention has been made from a consideration of the foregoing and seeks to provide a high strength paper and method of manufacturing such paper that overcome or mitigates at least some of the problems of the prior art.